/**
 * @file
 * MQTT client
 *
 * @defgroup mqtt MQTT client
 * @ingroup apps
 * @verbinclude mqtt_client.txt
 */

/*
 * Copyright (c) 2016 Erik Andersson <erian747@gmail.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack
 *
 * Author: Erik Andersson <erian747@gmail.com>
 *
 *
 * @todo:
 * - Handle large outgoing payloads for PUBLISH messages
 * - Fix restriction of a single topic in each (UN)SUBSCRIBE message (protocol has support for multiple topics)
 * - Add support for legacy MQTT protocol version
 *
 * Please coordinate changes and requests with Erik Andersson
 * Erik Andersson <erian747@gmail.com>
 *
 */
#include "lwip/apps/mqtt.h"
#include "lwip/timeouts.h"
#include "lwip/ip_addr.h"
#include "lwip/mem.h"
#include "lwip/err.h"
#include "lwip/pbuf.h"
#include "lwip/tcp.h"
#include <string.h>

#if LWIP_TCP && LWIP_CALLBACK_API

/**
 * MQTT_DEBUG: Default is off.
 */
#if !defined MQTT_DEBUG || defined __DOXYGEN__
#define MQTT_DEBUG                  LWIP_DBG_OFF
#endif

#define MQTT_DEBUG_TRACE        (MQTT_DEBUG | LWIP_DBG_TRACE)
#define MQTT_DEBUG_STATE        (MQTT_DEBUG | LWIP_DBG_STATE)
#define MQTT_DEBUG_WARN         (MQTT_DEBUG | LWIP_DBG_LEVEL_WARNING)
#define MQTT_DEBUG_WARN_STATE   (MQTT_DEBUG | LWIP_DBG_LEVEL_WARNING | LWIP_DBG_STATE)
#define MQTT_DEBUG_SERIOUS      (MQTT_DEBUG | LWIP_DBG_LEVEL_SERIOUS)

static void mqtt_cyclic_timer(void *arg);

/**
 * MQTT client connection states
 */
enum
{
    TCP_DISCONNECTED,
    TCP_CONNECTING,
    MQTT_CONNECTING,
    MQTT_CONNECTED
};

/**
 * MQTT control message types
 */
enum mqtt_message_type
{
    MQTT_MSG_TYPE_CONNECT = 1,
    MQTT_MSG_TYPE_CONNACK = 2,
    MQTT_MSG_TYPE_PUBLISH = 3,
    MQTT_MSG_TYPE_PUBACK = 4,
    MQTT_MSG_TYPE_PUBREC = 5,
    MQTT_MSG_TYPE_PUBREL = 6,
    MQTT_MSG_TYPE_PUBCOMP = 7,
    MQTT_MSG_TYPE_SUBSCRIBE = 8,
    MQTT_MSG_TYPE_SUBACK = 9,
    MQTT_MSG_TYPE_UNSUBSCRIBE = 10,
    MQTT_MSG_TYPE_UNSUBACK = 11,
    MQTT_MSG_TYPE_PINGREQ = 12,
    MQTT_MSG_TYPE_PINGRESP = 13,
    MQTT_MSG_TYPE_DISCONNECT = 14
};

/** Helpers to extract control packet type and qos from first byte in fixed header */
#define MQTT_CTL_PACKET_TYPE(fixed_hdr_byte0) ((fixed_hdr_byte0 & 0xf0) >> 4)
#define MQTT_CTL_PACKET_QOS(fixed_hdr_byte0) ((fixed_hdr_byte0 & 0x6) >> 1)

/**
 * MQTT connect flags, only used in CONNECT message
 */
enum mqtt_connect_flag
{
    MQTT_CONNECT_FLAG_USERNAME = 1 << 7,
    MQTT_CONNECT_FLAG_PASSWORD = 1 << 6,
    MQTT_CONNECT_FLAG_WILL_RETAIN = 1 << 5,
    MQTT_CONNECT_FLAG_WILL = 1 << 2,
    MQTT_CONNECT_FLAG_CLEAN_SESSION = 1 << 1
};


#if defined(LWIP_DEBUG)
static const char *const mqtt_message_type_str[15] =
{
    "UNDEFINED",
    "CONNECT",
    "CONNACK",
    "PUBLISH",
    "PUBACK",
    "PUBREC",
    "PUBREL",
    "PUBCOMP",
    "SUBSCRIBE",
    "SUBACK",
    "UNSUBSCRIBE",
    "UNSUBACK",
    "PINGREQ",
    "PINGRESP",
    "DISCONNECT"
};

/**
 * Message type value to string
 * @param msg_type see enum mqtt_message_type
 *
 * @return Control message type text string
 */
static const char *
mqtt_msg_type_to_str(u8_t msg_type)
{
    if (msg_type >= LWIP_ARRAYSIZE(mqtt_message_type_str))
    {
        msg_type = 0;
    }
    return mqtt_message_type_str[msg_type];
}

#endif


/**
 * Generate MQTT packet identifier
 * @param client MQTT client
 * @return New packet identifier, range 1 to 65535
 */
static u16_t
msg_generate_packet_id(mqtt_client_t *client)
{
    client->pkt_id_seq++;
    if (client->pkt_id_seq == 0)
    {
        client->pkt_id_seq++;
    }
    return client->pkt_id_seq;
}

/*--------------------------------------------------------------------------------------------------------------------- */
/* Output ring buffer */


#define MQTT_RINGBUF_IDX_MASK ((MQTT_OUTPUT_RINGBUF_SIZE) - 1)

/** Add single item to ring buffer */
#define mqtt_ringbuf_put(rb, item) ((rb)->buf)[(rb)->put++ & MQTT_RINGBUF_IDX_MASK] = (item)

/** Return number of bytes in ring buffer */
#define mqtt_ringbuf_len(rb) ((u16_t)((rb)->put - (rb)->get))

/** Return number of bytes free in ring buffer */
#define mqtt_ringbuf_free(rb) (MQTT_OUTPUT_RINGBUF_SIZE - mqtt_ringbuf_len(rb))

/** Return number of bytes possible to read without wrapping around */
#define mqtt_ringbuf_linear_read_length(rb) LWIP_MIN(mqtt_ringbuf_len(rb), (MQTT_OUTPUT_RINGBUF_SIZE - ((rb)->get & MQTT_RINGBUF_IDX_MASK)))

/** Return pointer to ring buffer get position */
#define mqtt_ringbuf_get_ptr(rb) (&(rb)->buf[(rb)->get & MQTT_RINGBUF_IDX_MASK])

#define mqtt_ringbuf_advance_get_idx(rb, len) ((rb)->get += (len))


/**
 * Try send as many bytes as possible from output ring buffer
 * @param rb Output ring buffer
 * @param tpcb TCP connection handle
 */
static void
mqtt_output_send(struct mqtt_ringbuf_t *rb, struct tcp_pcb *tpcb)
{
    err_t err;
    u8_t wrap = 0;
    u16_t ringbuf_lin_len = mqtt_ringbuf_linear_read_length(rb);
    u16_t send_len = tcp_sndbuf(tpcb);
    LWIP_ASSERT("mqtt_output_send: tpcb != NULL", tpcb != NULL);

    if (send_len == 0 || ringbuf_lin_len == 0)
    {
        return;
    }

    LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_output_send: tcp_sndbuf: %d bytes, ringbuf_linear_available: %d, get %d, put %d\n",
                                   send_len, ringbuf_lin_len, ((rb)->get & MQTT_RINGBUF_IDX_MASK), ((rb)->put & MQTT_RINGBUF_IDX_MASK)));

    if (send_len > ringbuf_lin_len)
    {
        /* Space in TCP output buffer is larger than available in ring buffer linear portion */
        send_len = ringbuf_lin_len;
        /* Wrap around if more data in ring buffer after linear portion */
        wrap = (mqtt_ringbuf_len(rb) > ringbuf_lin_len);
    }
    err = tcp_write(tpcb, mqtt_ringbuf_get_ptr(rb), send_len, TCP_WRITE_FLAG_COPY | (wrap ? TCP_WRITE_FLAG_MORE : 0));
    if ((err == ERR_OK) && wrap)
    {
        mqtt_ringbuf_advance_get_idx(rb, send_len);
        /* Use the lesser one of ring buffer linear length and TCP send buffer size */
        send_len = LWIP_MIN(tcp_sndbuf(tpcb), mqtt_ringbuf_linear_read_length(rb));
        err = tcp_write(tpcb, mqtt_ringbuf_get_ptr(rb), send_len, TCP_WRITE_FLAG_COPY);
    }

    if (err == ERR_OK)
    {
        mqtt_ringbuf_advance_get_idx(rb, send_len);
        /* Flush */
        tcp_output(tpcb);
    }
    else
    {
        LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_output_send: Send failed with err %d (\"%s\")\n", err, lwip_strerr(err)));
    }
}



/*--------------------------------------------------------------------------------------------------------------------- */
/* Request queue */

/**
 * Create request item
 * @param r_objs Pointer to request objects
 * @param pkt_id Packet identifier of request
 * @param cb Packet callback to call when requests lifetime ends
 * @param arg Parameter following callback
 * @return Request or NULL if failed to create
 */
static struct mqtt_request_t *
mqtt_create_request(struct mqtt_request_t *r_objs, u16_t pkt_id, mqtt_request_cb_t cb, void *arg)
{
    struct mqtt_request_t *r = NULL;
    u8_t n;
    LWIP_ASSERT("mqtt_create_request: r_objs != NULL", r_objs != NULL);
    for (n = 0; n < MQTT_REQ_MAX_IN_FLIGHT; n++)
    {
        /* Item point to itself if not in use */
        if (r_objs[n].next == &r_objs[n])
        {
            r = &r_objs[n];
            r->next = NULL;
            r->cb = cb;
            r->arg = arg;
            r->pkt_id = pkt_id;
            break;
        }
    }
    return r;
}


/**
 * Append request to pending request queue
 * @param tail Pointer to request queue tail pointer
 * @param r Request to append
 */
static void
mqtt_append_request(struct mqtt_request_t **tail, struct mqtt_request_t *r)
{
    struct mqtt_request_t *head = NULL;
    s16_t time_before = 0;
    struct mqtt_request_t *iter;

    LWIP_ASSERT("mqtt_append_request: tail != NULL", tail != NULL);

    /* Iterate trough queue to find head, and count total timeout time */
    for (iter = *tail; iter != NULL; iter = iter->next)
    {
        time_before += iter->timeout_diff;
        head = iter;
    }

    LWIP_ASSERT("mqtt_append_request: time_before <= MQTT_REQ_TIMEOUT", time_before <= MQTT_REQ_TIMEOUT);
    r->timeout_diff = MQTT_REQ_TIMEOUT - time_before;
    if (head == NULL)
    {
        *tail = r;
    }
    else
    {
        head->next = r;
    }
}


/**
 * Delete request item
 * @param r Request item to delete
 */
static void
mqtt_delete_request(struct mqtt_request_t *r)
{
    if (r != NULL)
    {
        r->next = r;
    }
}

/**
 * Remove a request item with a specific packet identifier from request queue
 * @param tail Pointer to request queue tail pointer
 * @param pkt_id Packet identifier of request to take
 * @return Request item if found, NULL if not
 */
static struct mqtt_request_t *
mqtt_take_request(struct mqtt_request_t **tail, u16_t pkt_id)
{
    struct mqtt_request_t *iter = NULL, *prev = NULL;
    LWIP_ASSERT("mqtt_take_request: tail != NULL", tail != NULL);
    /* Search all request for pkt_id */
    for (iter = *tail; iter != NULL; iter = iter->next)
    {
        if (iter->pkt_id == pkt_id)
        {
            break;
        }
        prev = iter;
    }

    /* If request was found */
    if (iter != NULL)
    {
        /* unchain */
        if (prev == NULL)
        {
            *tail = iter->next;
        }
        else
        {
            prev->next = iter->next;
        }
        /* If exists, add remaining timeout time for the request to next */
        if (iter->next != NULL)
        {
            iter->next->timeout_diff += iter->timeout_diff;
        }
        iter->next = NULL;
    }
    return iter;
}

/**
 * Handle requests timeout
 * @param tail Pointer to request queue tail pointer
 * @param t Time since last call in seconds
 */
static void
mqtt_request_time_elapsed(struct mqtt_request_t **tail, u8_t t)
{
    struct mqtt_request_t *r = *tail;
    LWIP_ASSERT("mqtt_request_time_elapsed: tail != NULL", tail != NULL);
    while (t > 0 && r != NULL)
    {
        if (t >= r->timeout_diff)
        {
            t -= (u8_t)r->timeout_diff;
            /* Unchain */
            *tail = r->next;
            /* Notify upper layer about timeout */
            if (r->cb != NULL)
            {
                r->cb(r->arg, ERR_TIMEOUT);
            }
            mqtt_delete_request(r);
            /* Tail might be be modified in callback, so re-read it in every iteration */
            r = *(struct mqtt_request_t *const volatile *)tail;
        }
        else
        {
            r->timeout_diff -= t;
            t = 0;
        }
    }
}

/**
 * Free all request items
 * @param tail Pointer to request queue tail pointer
 */
static void
mqtt_clear_requests(struct mqtt_request_t **tail)
{
    struct mqtt_request_t *iter, *next;
    LWIP_ASSERT("mqtt_clear_requests: tail != NULL", tail != NULL);
    for (iter = *tail; iter != NULL; iter = next)
    {
        next = iter->next;
        mqtt_delete_request(iter);
    }
    *tail = NULL;
}
/**
 * Initialize all request items
 * @param r_objs Pointer to request objects
 */
static void
mqtt_init_requests(struct mqtt_request_t *r_objs)
{
    u8_t n;
    LWIP_ASSERT("mqtt_init_requests: r_objs != NULL", r_objs != NULL);
    for (n = 0; n < MQTT_REQ_MAX_IN_FLIGHT; n++)
    {
        /* Item pointing to itself indicates unused */
        r_objs[n].next = &r_objs[n];
    }
}

/*--------------------------------------------------------------------------------------------------------------------- */
/* Output message build helpers */


static void
mqtt_output_append_u8(struct mqtt_ringbuf_t *rb, u8_t value)
{
    mqtt_ringbuf_put(rb, value);
}

static
void mqtt_output_append_u16(struct mqtt_ringbuf_t *rb, u16_t value)
{
    mqtt_ringbuf_put(rb, value >> 8);
    mqtt_ringbuf_put(rb, value & 0xff);
}

static void
mqtt_output_append_buf(struct mqtt_ringbuf_t *rb, const void *data, u16_t length)
{
    u16_t n;
    for (n = 0; n < length; n++)
    {
        mqtt_ringbuf_put(rb, ((const u8_t *)data)[n]);
    }
}

static void
mqtt_output_append_string(struct mqtt_ringbuf_t *rb, const char *str, u16_t length)
{
    u16_t n;
    mqtt_ringbuf_put(rb, length >> 8);
    mqtt_ringbuf_put(rb, length & 0xff);
    for (n = 0; n < length; n++)
    {
        mqtt_ringbuf_put(rb, str[n]);
    }
}

/**
 * Append fixed header
 * @param rb Output ring buffer
 * @param msg_type see enum mqtt_message_type
 * @param dup MQTT DUP flag
 * @param qos MQTT QoS field
 * @param retain MQTT retain flag
 * @param r_length Remaining length after fixed header
 */

static void
mqtt_output_append_fixed_header(struct mqtt_ringbuf_t *rb, u8_t msg_type, u8_t dup,
                                u8_t qos, u8_t retain, u16_t r_length)
{
    /* Start with control byte */
    mqtt_output_append_u8(rb, (((msg_type & 0x0f) << 4) | ((dup & 1) << 3) | ((qos & 3) << 1) | (retain & 1)));
    /* Encode remaining length field */
    do
    {
        mqtt_output_append_u8(rb, (r_length & 0x7f) | (r_length >= 128 ? 0x80 : 0));
        r_length >>= 7;
    }
    while (r_length > 0);
}


/**
 * Check output buffer space
 * @param rb Output ring buffer
 * @param r_length Remaining length after fixed header
 * @return 1 if message will fit, 0 if not enough buffer space
 */
static u8_t
mqtt_output_check_space(struct mqtt_ringbuf_t *rb, u16_t r_length)
{
    /* Start with length of type byte + remaining length */
    u16_t total_len = 1 + r_length;

    LWIP_ASSERT("mqtt_output_check_space: rb != NULL", rb != NULL);

    /* Calculate number of required bytes to contain the remaining bytes field and add to total*/
    do
    {
        total_len++;
        r_length >>= 7;
    }
    while (r_length > 0);

    return (total_len <= mqtt_ringbuf_free(rb));
}


/**
 * Close connection to server
 * @param client MQTT client
 * @param reason Reason for disconnection
 */
static void
mqtt_close(mqtt_client_t *client, mqtt_connection_status_t reason)
{
    LWIP_ASSERT("mqtt_close: client != NULL", client != NULL);

    /* Bring down TCP connection if not already done */
    if (client->conn != NULL)
    {
        err_t res;
        tcp_recv(client->conn, NULL);
        tcp_err(client->conn,  NULL);
        tcp_sent(client->conn, NULL);
        res = tcp_close(client->conn);
        if (res != ERR_OK)
        {
            tcp_abort(client->conn);
            LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_close: Close err=%s\n", lwip_strerr(res)));
        }
        client->conn = NULL;
    }

    /* Remove all pending requests */
    mqtt_clear_requests(&client->pend_req_queue);
    /* Stop cyclic timer */
    sys_untimeout(mqtt_cyclic_timer, client);

    /* Notify upper layer of disconnection if changed state */
    if (client->conn_state != TCP_DISCONNECTED)
    {

        client->conn_state = TCP_DISCONNECTED;
        if (client->connect_cb != NULL)
        {
            client->connect_cb(client, client->connect_arg, reason);
        }
    }
}


/**
 * Interval timer, called every MQTT_CYCLIC_TIMER_INTERVAL seconds in MQTT_CONNECTING and MQTT_CONNECTED states
 * @param arg MQTT client
 */
static void
mqtt_cyclic_timer(void *arg)
{
    u8_t restart_timer = 1;
    mqtt_client_t *client = (mqtt_client_t *)arg;
    LWIP_ASSERT("mqtt_cyclic_timer: client != NULL", client != NULL);

    if (client->conn_state == MQTT_CONNECTING)
    {
        client->cyclic_tick++;
        if ((client->cyclic_tick * MQTT_CYCLIC_TIMER_INTERVAL) >= MQTT_CONNECT_TIMOUT)
        {
            LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_cyclic_timer: CONNECT attempt to server timed out\n"));
            /* Disconnect TCP */
            mqtt_close(client, MQTT_CONNECT_TIMEOUT);
            restart_timer = 0;
        }
    }
    else if (client->conn_state == MQTT_CONNECTED)
    {
        /* Handle timeout for pending requests */
        mqtt_request_time_elapsed(&client->pend_req_queue, MQTT_CYCLIC_TIMER_INTERVAL);

        /* keep_alive > 0 means keep alive functionality shall be used */
        if (client->keep_alive > 0)
        {

            client->server_watchdog++;
            /* If reception from server has been idle for 1.5*keep_alive time, server is considered unresponsive */
            if ((client->server_watchdog * MQTT_CYCLIC_TIMER_INTERVAL) > (client->keep_alive + client->keep_alive / 2))
            {
                LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_cyclic_timer: Server incoming keep-alive timeout\n"));
                mqtt_close(client, MQTT_CONNECT_TIMEOUT);
                restart_timer = 0;
            }

            /* If time for a keep alive message to be sent, transmission has been idle for keep_alive time */
            if ((client->cyclic_tick * MQTT_CYCLIC_TIMER_INTERVAL) >= client->keep_alive)
            {
                LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_cyclic_timer: Sending keep-alive message to server\n"));
                if (mqtt_output_check_space(&client->output, 0) != 0)
                {
                    mqtt_output_append_fixed_header(&client->output, MQTT_MSG_TYPE_PINGREQ, 0, 0, 0, 0);
                    client->cyclic_tick = 0;
                }
            }
            else
            {
                client->cyclic_tick++;
            }
        }
    }
    else
    {
        LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_cyclic_timer: Timer should not be running in state %d\n", client->conn_state));
        restart_timer = 0;
    }
    if (restart_timer)
    {
        sys_timeout(MQTT_CYCLIC_TIMER_INTERVAL * 1000, mqtt_cyclic_timer, arg);
    }
}


/**
 * Send PUBACK, PUBREC or PUBREL response message
 * @param client MQTT client
 * @param msg PUBACK, PUBREC or PUBREL
 * @param pkt_id Packet identifier
 * @param qos QoS value
 * @return ERR_OK if successful, ERR_MEM if out of memory
 */
static err_t
pub_ack_rec_rel_response(mqtt_client_t *client, u8_t msg, u16_t pkt_id, u8_t qos)
{
    err_t err = ERR_OK;
    if (mqtt_output_check_space(&client->output, 2))
    {
        mqtt_output_append_fixed_header(&client->output, msg, 0, qos, 0, 2);
        mqtt_output_append_u16(&client->output, pkt_id);
        mqtt_output_send(&client->output, client->conn);
    }
    else
    {
        LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("pub_ack_rec_rel_response: OOM creating response: %s with pkt_id: %d\n",
                                       mqtt_msg_type_to_str(msg), pkt_id));
        err = ERR_MEM;
    }
    return err;
}

/**
 * Subscribe response from server
 * @param r Matching request
 * @param result Result code from server
 */
static void
mqtt_incomming_suback(struct mqtt_request_t *r, u8_t result)
{
    if (r->cb != NULL)
    {
        r->cb(r->arg, result < 3 ? ERR_OK : ERR_ABRT);
    }
}


/**
 * Complete MQTT message received or buffer full
 * @param client MQTT client
 * @param fixed_hdr_idx header index
 * @param length length received part
 * @param remaining_length Remaining length of complete message
 */
static mqtt_connection_status_t
mqtt_message_received(mqtt_client_t *client, u8_t fixed_hdr_idx, u16_t length, u32_t remaining_length)
{
    mqtt_connection_status_t res = MQTT_CONNECT_ACCEPTED;

    u8_t *var_hdr_payload = client->rx_buffer + fixed_hdr_idx;

    /* Control packet type */
    u8_t pkt_type = MQTT_CTL_PACKET_TYPE(client->rx_buffer[0]);
    u16_t pkt_id = 0;

    if (pkt_type == MQTT_MSG_TYPE_CONNACK)
    {
        if (client->conn_state == MQTT_CONNECTING)
        {
            /* Get result code from CONNACK */
            res = (mqtt_connection_status_t)var_hdr_payload[1];
            LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_message_received: Connect response code %d\n", res));
            if (res == MQTT_CONNECT_ACCEPTED)
            {
                /* Reset cyclic_tick when changing to connected state */
                client->cyclic_tick = 0;
                client->conn_state = MQTT_CONNECTED;
                /* Notify upper layer */
                if (client->connect_cb != 0)
                {
                    client->connect_cb(client, client->connect_arg, res);
                }
            }
        }
        else
        {
            LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_message_received: Received CONNACK in connected state\n"));
        }
    }
    else if (pkt_type == MQTT_MSG_TYPE_PINGRESP)
    {
        LWIP_DEBUGF(MQTT_DEBUG_TRACE, ( "mqtt_message_received: Received PINGRESP from server\n"));

    }
    else if (pkt_type == MQTT_MSG_TYPE_PUBLISH)
    {
        u16_t payload_offset = 0;
        u16_t payload_length = length;
        u8_t qos = MQTT_CTL_PACKET_QOS(client->rx_buffer[0]);

        if (client->msg_idx <= MQTT_VAR_HEADER_BUFFER_LEN)
        {
            /* Should have topic and pkt id*/
            uint8_t *topic;
            uint16_t after_topic;
            u8_t bkp;
            u16_t topic_len = var_hdr_payload[0];
            topic_len = (topic_len << 8) + (u16_t)(var_hdr_payload[1]);

            topic = var_hdr_payload + 2;
            after_topic = 2 + topic_len;
            /* Check length, add one byte even for QoS 0 so that zero termination will fit */
            if ((after_topic + (qos ? 2 : 1)) > length)
            {
                LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_message_received: Receive buffer can not fit topic + pkt_id\n"));
                goto out_disconnect;
            }

            /* id for QoS 1 and 2 */
            if (qos > 0)
            {
                client->inpub_pkt_id = ((u16_t)var_hdr_payload[after_topic] << 8) + (u16_t)var_hdr_payload[after_topic + 1];
                after_topic += 2;
            }
            else
            {
                client->inpub_pkt_id = 0;
            }
            /* Take backup of byte after topic */
            bkp = topic[topic_len];
            /* Zero terminate string */
            topic[topic_len] = 0;
            /* Payload data remaining in receive buffer */
            payload_length = length - after_topic;
            payload_offset = after_topic;

            LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_incomming_publish: Received message with QoS %d at topic: %s, payload length %d\n",
                                           qos, topic, remaining_length + payload_length));
            if (client->pub_cb != NULL)
            {
                client->pub_cb(client->inpub_arg, (const char *)topic, remaining_length + payload_length);
            }
            /* Restore byte after topic */
            topic[topic_len] = bkp;
        }
        if (payload_length > 0 || remaining_length == 0)
        {
            client->data_cb(client->inpub_arg, var_hdr_payload + payload_offset, payload_length, remaining_length == 0 ? MQTT_DATA_FLAG_LAST : 0);
            /* Reply if QoS > 0 */
            if (remaining_length == 0 && qos > 0)
            {
                /* Send PUBACK for QoS 1 or PUBREC for QoS 2 */
                u8_t resp_msg = (qos == 1) ? MQTT_MSG_TYPE_PUBACK : MQTT_MSG_TYPE_PUBREC;
                LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_incomming_publish: Sending publish response: %s with pkt_id: %d\n",
                                               mqtt_msg_type_to_str(resp_msg), client->inpub_pkt_id));
                pub_ack_rec_rel_response(client, resp_msg, client->inpub_pkt_id, 0);
            }
        }
    }
    else
    {
        /* Get packet identifier */
        pkt_id = (u16_t)var_hdr_payload[0] << 8;
        pkt_id |= (u16_t)var_hdr_payload[1];
        if (pkt_id == 0)
        {
            LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_message_received: Got message with illegal packet identifier: 0\n"));
            goto out_disconnect;
        }
        if (pkt_type == MQTT_MSG_TYPE_PUBREC)
        {
            LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_message_received: PUBREC, sending PUBREL with pkt_id: %d\n", pkt_id));
            pub_ack_rec_rel_response(client, MQTT_MSG_TYPE_PUBREL, pkt_id, 1);

        }
        else if (pkt_type == MQTT_MSG_TYPE_PUBREL)
        {
            LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_message_received: PUBREL, sending PUBCOMP response with pkt_id: %d\n", pkt_id));
            pub_ack_rec_rel_response(client, MQTT_MSG_TYPE_PUBCOMP, pkt_id, 0);

        }
        else if (pkt_type == MQTT_MSG_TYPE_SUBACK || pkt_type == MQTT_MSG_TYPE_UNSUBACK ||
                 pkt_type == MQTT_MSG_TYPE_PUBCOMP || pkt_type == MQTT_MSG_TYPE_PUBACK)
        {
            struct mqtt_request_t *r = mqtt_take_request(&client->pend_req_queue, pkt_id);
            if (r != NULL)
            {
                LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_message_received: %s response with id %d\n", mqtt_msg_type_to_str(pkt_type), pkt_id));
                if (pkt_type == MQTT_MSG_TYPE_SUBACK)
                {
                    if (length < 3)
                    {
                        LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_message_received: To small SUBACK packet\n"));
                        goto out_disconnect;
                    }
                    else
                    {
                        mqtt_incomming_suback(r, var_hdr_payload[2]);
                    }
                }
                else if (r->cb != NULL)
                {
                    r->cb(r->arg, ERR_OK);
                }
                mqtt_delete_request(r);
            }
            else
            {
                LWIP_DEBUGF(MQTT_DEBUG_WARN, ( "mqtt_message_received: Received %s reply, with wrong pkt_id: %d\n", mqtt_msg_type_to_str(pkt_type), pkt_id));
            }
        }
        else
        {
            LWIP_DEBUGF(MQTT_DEBUG_WARN, ( "mqtt_message_received: Received unknown message type: %d\n", pkt_type));
            goto out_disconnect;
        }
    }
    return res;
out_disconnect:
    return MQTT_CONNECT_DISCONNECTED;
}


/**
 * MQTT incoming message parser
 * @param client MQTT client
 * @param p PBUF chain of received data
 * @return Connection status
 */
static mqtt_connection_status_t
mqtt_parse_incoming(mqtt_client_t *client, struct pbuf *p)
{
    u16_t in_offset = 0;
    u32_t msg_rem_len = 0;
    u8_t fixed_hdr_idx = 0;
    u8_t b = 0;

    while (p->tot_len > in_offset)
    {
        if ((fixed_hdr_idx < 2) || ((b & 0x80) != 0))
        {

            if (fixed_hdr_idx < client->msg_idx)
            {
                b = client->rx_buffer[fixed_hdr_idx];
            }
            else
            {
                b = pbuf_get_at(p, in_offset++);
                client->rx_buffer[client->msg_idx++] = b;
            }
            fixed_hdr_idx++;

            if (fixed_hdr_idx >= 2)
            {
                msg_rem_len |= (u32_t)(b & 0x7f) << ((fixed_hdr_idx - 2) * 7);
                if ((b & 0x80) == 0)
                {
                    LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_parse_incoming: Remaining length after fixed header: %d\n", msg_rem_len));
                    if (msg_rem_len == 0)
                    {
                        /* Complete message with no extra headers of payload received */
                        mqtt_message_received(client, fixed_hdr_idx, 0, 0);
                        client->msg_idx = 0;
                        fixed_hdr_idx = 0;
                    }
                    else
                    {
                        /* Bytes remaining in message */
                        msg_rem_len = (msg_rem_len + fixed_hdr_idx) - client->msg_idx;
                    }
                }
            }
        }
        else
        {
            u16_t cpy_len, cpy_start, buffer_space;

            cpy_start = (client->msg_idx - fixed_hdr_idx) % (MQTT_VAR_HEADER_BUFFER_LEN - fixed_hdr_idx) + fixed_hdr_idx;

            /* Allow to copy the lesser one of available length in input data or bytes remaining in message */
            cpy_len = (u16_t)LWIP_MIN((u16_t)(p->tot_len - in_offset), msg_rem_len);

            /* Limit to available space in buffer */
            buffer_space = MQTT_VAR_HEADER_BUFFER_LEN - cpy_start;
            if (cpy_len > buffer_space)
            {
                cpy_len = buffer_space;
            }
            pbuf_copy_partial(p, client->rx_buffer + cpy_start, cpy_len, in_offset);

            /* Advance get and put indexes  */
            client->msg_idx += cpy_len;
            in_offset += cpy_len;
            msg_rem_len -= cpy_len;

            LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_parse_incoming: msg_idx: %d, cpy_len: %d, remaining %d\n", client->msg_idx, cpy_len, msg_rem_len));
            if (msg_rem_len == 0 || cpy_len == buffer_space)
            {
                /* Whole message received or buffer is full */
                mqtt_connection_status_t res = mqtt_message_received(client, fixed_hdr_idx, (cpy_start + cpy_len) - fixed_hdr_idx, msg_rem_len);
                if (res != MQTT_CONNECT_ACCEPTED)
                {
                    return res;
                }
                if (msg_rem_len == 0)
                {
                    /* Reset parser state */
                    client->msg_idx = 0;
                    /* msg_tot_len = 0; */
                    fixed_hdr_idx = 0;
                }
            }
        }
    }
    return MQTT_CONNECT_ACCEPTED;
}


/**
 * TCP received callback function. @see tcp_recv_fn
 * @param arg MQTT client
 * @param p PBUF chain of received data
 * @param err Passed as return value if not ERR_OK
 * @return ERR_OK or err passed into callback
 */
static err_t
mqtt_tcp_recv_cb(void *arg, struct tcp_pcb *pcb, struct pbuf *p, err_t err)
{
    mqtt_client_t *client = (mqtt_client_t *)arg;
    LWIP_ASSERT("mqtt_tcp_recv_cb: client != NULL", client != NULL);
    LWIP_ASSERT("mqtt_tcp_recv_cb: client->conn == pcb", client->conn == pcb);

    if (p == NULL)
    {
        LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_tcp_recv_cb: Recv pbuf=NULL, remote has closed connection\n"));
        mqtt_close(client, MQTT_CONNECT_DISCONNECTED);
    }
    else
    {
        mqtt_connection_status_t res;
        if (err != ERR_OK)
        {
            LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_tcp_recv_cb: Recv err=%d\n", err));
            pbuf_free(p);
            return err;
        }

        /* Tell remote that data has been received */
        tcp_recved(pcb, p->tot_len);
        res = mqtt_parse_incoming(client, p);
        pbuf_free(p);

        if (res != MQTT_CONNECT_ACCEPTED)
        {
            mqtt_close(client, res);
        }
        /* If keep alive functionality is used */
        if (client->keep_alive != 0)
        {
            /* Reset server alive watchdog */
            client->server_watchdog = 0;
        }

    }
    return ERR_OK;
}


/**
 * TCP data sent callback function. @see tcp_sent_fn
 * @param arg MQTT client
 * @param tpcb TCP connection handle
 * @param len Number of bytes sent
 * @return ERR_OK
 */
static err_t
mqtt_tcp_sent_cb(void *arg, struct tcp_pcb *tpcb, u16_t len)
{
    mqtt_client_t *client = (mqtt_client_t *)arg;

    LWIP_UNUSED_ARG(tpcb);
    LWIP_UNUSED_ARG(len);

    if (client->conn_state == MQTT_CONNECTED)
    {
        struct mqtt_request_t *r;

        /* Reset keep-alive send timer and server watchdog */
        client->cyclic_tick = 0;
        client->server_watchdog = 0;
        /* QoS 0 publish has no response from server, so call its callbacks here */
        while ((r = mqtt_take_request(&client->pend_req_queue, 0)) != NULL)
        {
            LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_tcp_sent_cb: Calling QoS 0 publish complete callback\n"));
            if (r->cb != NULL)
            {
                r->cb(r->arg, ERR_OK);
            }
            mqtt_delete_request(r);
        }
        /* Try send any remaining buffers from output queue */
        mqtt_output_send(&client->output, client->conn);
    }
    return ERR_OK;
}

/**
 * TCP error callback function. @see tcp_err_fn
 * @param arg MQTT client
 * @param err Error encountered
 */
static void
mqtt_tcp_err_cb(void *arg, err_t err)
{
    mqtt_client_t *client = (mqtt_client_t *)arg;
    LWIP_UNUSED_ARG(err); /* only used for debug output */
    LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_tcp_err_cb: TCP error callback: error %d, arg: %p\n", err, arg));
    LWIP_ASSERT("mqtt_tcp_err_cb: client != NULL", client != NULL);
    /* Set conn to null before calling close as pcb is already deallocated*/
    client->conn = 0;
    mqtt_close(client, MQTT_CONNECT_DISCONNECTED);
}

/**
 * TCP poll callback function. @see tcp_poll_fn
 * @param arg MQTT client
 * @param tpcb TCP connection handle
 * @return err ERR_OK
 */
static err_t
mqtt_tcp_poll_cb(void *arg, struct tcp_pcb *tpcb)
{
    mqtt_client_t *client = (mqtt_client_t *)arg;
    if (client->conn_state == MQTT_CONNECTED)
    {
        /* Try send any remaining buffers from output queue */
        mqtt_output_send(&client->output, tpcb);
    }
    return ERR_OK;
}

/**
 * TCP connect callback function. @see tcp_connected_fn
 * @param arg MQTT client
 * @param err Always ERR_OK, mqtt_tcp_err_cb is called in case of error
 * @return ERR_OK
 */
static err_t
mqtt_tcp_connect_cb(void *arg, struct tcp_pcb *tpcb, err_t err)
{
    mqtt_client_t *client = (mqtt_client_t *)arg;

    if (err != ERR_OK)
    {
        LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_tcp_connect_cb: TCP connect error %d\n", err));
        return err;
    }

    /* Initiate receiver state */
    client->msg_idx = 0;

    /* Setup TCP callbacks */
    tcp_recv(tpcb, mqtt_tcp_recv_cb);
    tcp_sent(tpcb, mqtt_tcp_sent_cb);
    tcp_poll(tpcb, mqtt_tcp_poll_cb, 2);

    LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_tcp_connect_cb: TCP connection established to server\n"));
    /* Enter MQTT connect state */
    client->conn_state = MQTT_CONNECTING;

    /* Start cyclic timer */
    sys_timeout(MQTT_CYCLIC_TIMER_INTERVAL * 1000, mqtt_cyclic_timer, client);
    client->cyclic_tick = 0;

    /* Start transmission from output queue, connect message is the first one out*/
    mqtt_output_send(&client->output, client->conn);

    return ERR_OK;
}



/*---------------------------------------------------------------------------------------------------- */
/* Public API */


/**
 * @ingroup mqtt
 * MQTT publish function.
 * @param client MQTT client
 * @param topic Publish topic string
 * @param payload Data to publish (NULL is allowed)
 * @param payload_length: Length of payload (0 is allowed)
 * @param qos Quality of service, 0 1 or 2
 * @param retain MQTT retain flag
 * @param cb Callback to call when publish is complete or has timed out
 * @param arg User supplied argument to publish callback
 * @return ERR_OK if successful
 *         ERR_CONN if client is disconnected
 *         ERR_MEM if short on memory
 */
err_t
mqtt_publish(mqtt_client_t *client, const char *topic, const void *payload, u16_t payload_length, u8_t qos, u8_t retain,
             mqtt_request_cb_t cb, void *arg)
{
    struct mqtt_request_t *r;
    u16_t pkt_id;
    size_t topic_strlen;
    size_t total_len;
    u16_t topic_len;
    u16_t remaining_length;

    LWIP_ASSERT("mqtt_publish: client != NULL", client);
    LWIP_ASSERT("mqtt_publish: topic != NULL", topic);
    LWIP_ERROR("mqtt_publish: TCP disconnected", (client->conn_state != TCP_DISCONNECTED), return ERR_CONN);

    topic_strlen = strlen(topic);
    LWIP_ERROR("mqtt_publish: topic length overflow", (topic_strlen <= (0xFFFF - 2)), return ERR_ARG);
    topic_len = (u16_t)topic_strlen;
    total_len = 2 + topic_len + payload_length;
    LWIP_ERROR("mqtt_publish: total length overflow", (total_len <= 0xFFFF), return ERR_ARG);
    remaining_length = (u16_t)total_len;

    LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_publish: Publish with payload length %d to topic \"%s\"\n", payload_length, topic));

    if (qos > 0)
    {
        remaining_length += 2;
        /* Generate pkt_id id for QoS1 and 2 */
        pkt_id = msg_generate_packet_id(client);
    }
    else
    {
        /* Use reserved value pkt_id 0 for QoS 0 in request handle */
        pkt_id = 0;
    }

    r = mqtt_create_request(client->req_list, pkt_id, cb, arg);
    if (r == NULL)
    {
        return ERR_MEM;
    }

    if (mqtt_output_check_space(&client->output, remaining_length) == 0)
    {
        mqtt_delete_request(r);
        return ERR_MEM;
    }
    /* Append fixed header */
    mqtt_output_append_fixed_header(&client->output, MQTT_MSG_TYPE_PUBLISH, 0, qos, retain, remaining_length);

    /* Append Topic */
    mqtt_output_append_string(&client->output, topic, topic_len);

    /* Append packet if for QoS 1 and 2*/
    if (qos > 0)
    {
        mqtt_output_append_u16(&client->output, pkt_id);
    }

    /* Append optional publish payload */
    if ((payload != NULL) && (payload_length > 0))
    {
        mqtt_output_append_buf(&client->output, payload, payload_length);
    }

    mqtt_append_request(&client->pend_req_queue, r);
    mqtt_output_send(&client->output, client->conn);
    return ERR_OK;
}


/**
 * @ingroup mqtt
 * MQTT subscribe/unsubscribe function.
 * @param client MQTT client
 * @param topic topic to subscribe to
 * @param qos Quality of service, 0 1 or 2 (only used for subscribe)
 * @param cb Callback to call when subscribe/unsubscribe reponse is received
 * @param arg User supplied argument to publish callback
 * @param sub 1 for subscribe, 0 for unsubscribe
 * @return ERR_OK if successful, @see err_t enum for other results
 */
err_t
mqtt_sub_unsub(mqtt_client_t *client, const char *topic, u8_t qos, mqtt_request_cb_t cb, void *arg, u8_t sub)
{
    size_t topic_strlen;
    size_t total_len;
    u16_t topic_len;
    u16_t remaining_length;
    u16_t pkt_id;
    struct mqtt_request_t *r;

    LWIP_ASSERT("mqtt_sub_unsub: client != NULL", client);
    LWIP_ASSERT("mqtt_sub_unsub: topic != NULL", topic);

    topic_strlen = strlen(topic);
    LWIP_ERROR("mqtt_sub_unsub: topic length overflow", (topic_strlen <= (0xFFFF - 2)), return ERR_ARG);
    topic_len = (u16_t)topic_strlen;
    /* Topic string, pkt_id, qos for subscribe */
    total_len =  topic_len + 2 + 2 + (sub != 0);
    LWIP_ERROR("mqtt_sub_unsub: total length overflow", (total_len <= 0xFFFF), return ERR_ARG);
    remaining_length = (u16_t)total_len;

    LWIP_ASSERT("mqtt_sub_unsub: qos < 3", qos < 3);
    if (client->conn_state == TCP_DISCONNECTED)
    {
        LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_sub_unsub: Can not (un)subscribe in disconnected state\n"));
        return ERR_CONN;
    }

    pkt_id = msg_generate_packet_id(client);
    r = mqtt_create_request(client->req_list, pkt_id, cb, arg);
    if (r == NULL)
    {
        return ERR_MEM;
    }

    if (mqtt_output_check_space(&client->output, remaining_length) == 0)
    {
        mqtt_delete_request(r);
        return ERR_MEM;
    }

    LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_sub_unsub: Client (un)subscribe to topic \"%s\", id: %d\n", topic, pkt_id));

    mqtt_output_append_fixed_header(&client->output, sub ? MQTT_MSG_TYPE_SUBSCRIBE : MQTT_MSG_TYPE_UNSUBSCRIBE, 0, 1, 0, remaining_length);
    /* Packet id */
    mqtt_output_append_u16(&client->output, pkt_id);
    /* Topic */
    mqtt_output_append_string(&client->output, topic, topic_len);
    /* QoS */
    if (sub != 0)
    {
        mqtt_output_append_u8(&client->output, LWIP_MIN(qos, 2));
    }

    mqtt_append_request(&client->pend_req_queue, r);
    mqtt_output_send(&client->output, client->conn);
    return ERR_OK;
}


/**
 * @ingroup mqtt
 * Set callback to handle incoming publish requests from server
 * @param client MQTT client
 * @param pub_cb Callback invoked when publish starts, contain topic and total length of payload
 * @param data_cb Callback for each fragment of payload that arrives
 * @param arg User supplied argument to both callbacks
 */
void
mqtt_set_inpub_callback(mqtt_client_t *client, mqtt_incoming_publish_cb_t pub_cb,
                        mqtt_incoming_data_cb_t data_cb, void *arg)
{
    LWIP_ASSERT("mqtt_set_inpub_callback: client != NULL", client != NULL);
    client->data_cb = data_cb;
    client->pub_cb = pub_cb;
    client->inpub_arg = arg;
}

/**
 * @ingroup mqtt
 * Create a new MQTT client instance
 * @return Pointer to instance on success, NULL otherwise
 */
mqtt_client_t *
mqtt_client_new(void)
{
    mqtt_client_t *client = (mqtt_client_t *)mem_malloc(sizeof(mqtt_client_t));
    if (client != NULL)
    {
        memset(client, 0, sizeof(mqtt_client_t));
    }
    return client;
}


/**
 * @ingroup mqtt
 * Connect to MQTT server
 * @param client MQTT client
 * @param ip_addr Server IP
 * @param port Server port
 * @param cb Connection state change callback
 * @param arg User supplied argument to connection callback
 * @param client_info Client identification and connection options
 * @return ERR_OK if successful, @see err_t enum for other results
 */
err_t
mqtt_client_connect(mqtt_client_t *client, const ip_addr_t *ip_addr, u16_t port, mqtt_connection_cb_t cb, void *arg,
                    const struct mqtt_connect_client_info_t *client_info)
{
    err_t err;
    size_t len;
    u16_t client_id_length;
    /* Length is the sum of 2+"MQTT", protocol level, flags and keep alive */
    u16_t remaining_length = 2 + 4 + 1 + 1 + 2;
    u8_t flags = 0, will_topic_len = 0, will_msg_len = 0;

    LWIP_ASSERT("mqtt_client_connect: client != NULL", client != NULL);
    LWIP_ASSERT("mqtt_client_connect: ip_addr != NULL", ip_addr != NULL);
    LWIP_ASSERT("mqtt_client_connect: client_info != NULL", client_info != NULL);
    LWIP_ASSERT("mqtt_client_connect: client_info->client_id != NULL", client_info->client_id != NULL);

    if (client->conn_state != TCP_DISCONNECTED)
    {
        LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_client_connect: Already connected\n"));
        return ERR_ISCONN;
    }

    /* Wipe clean */
    memset(client, 0, sizeof(mqtt_client_t));
    client->connect_arg = arg;
    client->connect_cb = cb;
    client->keep_alive = client_info->keep_alive;
    mqtt_init_requests(client->req_list);

    /* Build connect message */
    if (client_info->will_topic != NULL && client_info->will_msg != NULL)
    {
        flags |= MQTT_CONNECT_FLAG_WILL;
        flags |= (client_info->will_qos & 3) << 3;
        if (client_info->will_retain)
        {
            flags |= MQTT_CONNECT_FLAG_WILL_RETAIN;
        }
        len = strlen(client_info->will_topic);
        LWIP_ERROR("mqtt_client_connect: client_info->will_topic length overflow", len <= 0xFF, return ERR_VAL);
        LWIP_ERROR("mqtt_client_connect: client_info->will_topic length must be > 0", len > 0, return ERR_VAL);
        will_topic_len = (u8_t)len;
        len = strlen(client_info->will_msg);
        LWIP_ERROR("mqtt_client_connect: client_info->will_msg length overflow", len <= 0xFF, return ERR_VAL);
        will_msg_len = (u8_t)len;
        len = remaining_length + 2 + will_topic_len + 2 + will_msg_len;
        LWIP_ERROR("mqtt_client_connect: remaining_length overflow", len <= 0xFFFF, return ERR_VAL);
        remaining_length = (u16_t)len;
    }

    /* Don't complicate things, always connect using clean session */
    flags |= MQTT_CONNECT_FLAG_CLEAN_SESSION;

    len = strlen(client_info->client_id);
    LWIP_ERROR("mqtt_client_connect: client_info->client_id length overflow", len <= 0xFFFF, return ERR_VAL);
    client_id_length = (u16_t)len;
    len = remaining_length + 2 + client_id_length;
    LWIP_ERROR("mqtt_client_connect: remaining_length overflow", len <= 0xFFFF, return ERR_VAL);
    remaining_length = (u16_t)len;

    if (mqtt_output_check_space(&client->output, remaining_length) == 0)
    {
        return ERR_MEM;
    }

    client->conn = tcp_new();
    if (client->conn == NULL)
    {
        return ERR_MEM;
    }

    /* Set arg pointer for callbacks */
    tcp_arg(client->conn, client);
    /* Any local address, pick random local port number */
    err = tcp_bind(client->conn, IP_ADDR_ANY, 0);
    if (err != ERR_OK)
    {
        LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_client_connect: Error binding to local ip/port, %d\n", err));
        goto tcp_fail;
    }
    LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_client_connect: Connecting to host: %s at port:%"U16_F"\n", ipaddr_ntoa(ip_addr), port));

    /* Connect to server */
    err = tcp_connect(client->conn, ip_addr, port, mqtt_tcp_connect_cb);
    if (err != ERR_OK)
    {
        LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_client_connect: Error connecting to remote ip/port, %d\n", err));
        goto tcp_fail;
    }
    /* Set error callback */
    tcp_err(client->conn, mqtt_tcp_err_cb);
    client->conn_state = TCP_CONNECTING;

    /* Append fixed header */
    mqtt_output_append_fixed_header(&client->output, MQTT_MSG_TYPE_CONNECT, 0, 0, 0, remaining_length);
    /* Append Protocol string */
    mqtt_output_append_string(&client->output, "MQTT", 4);
    /* Append Protocol level */
    mqtt_output_append_u8(&client->output, 4);
    /* Append connect flags */
    mqtt_output_append_u8(&client->output, flags);
    /* Append keep-alive */
    mqtt_output_append_u16(&client->output, client_info->keep_alive);
    /* Append client id */
    mqtt_output_append_string(&client->output, client_info->client_id, client_id_length);
    /* Append will message if used */
    if ((flags & MQTT_CONNECT_FLAG_WILL) != 0)
    {
        mqtt_output_append_string(&client->output, client_info->will_topic, will_topic_len);
        mqtt_output_append_string(&client->output, client_info->will_msg, will_msg_len);
    }
    return ERR_OK;

tcp_fail:
    tcp_abort(client->conn);
    client->conn = NULL;
    return err;
}


/**
 * @ingroup mqtt
 * Disconnect from MQTT server
 * @param client MQTT client
 */
void
mqtt_disconnect(mqtt_client_t *client)
{
    LWIP_ASSERT("mqtt_disconnect: client != NULL", client);
    /* If connection in not already closed */
    if (client->conn_state != TCP_DISCONNECTED)
    {
        /* Set conn_state before calling mqtt_close to prevent callback from being called */
        client->conn_state = TCP_DISCONNECTED;
        mqtt_close(client, (mqtt_connection_status_t)0);
    }
}

/**
 * @ingroup mqtt
 * Check connection with server
 * @param client MQTT client
 * @return 1 if connected to server, 0 otherwise
 */
u8_t
mqtt_client_is_connected(mqtt_client_t *client)
{
    LWIP_ASSERT("mqtt_client_is_connected: client != NULL", client);
    return client->conn_state == MQTT_CONNECTED;
}

#endif /* LWIP_TCP && LWIP_CALLBACK_API */
